Currently marketed domestic spray devices predominately use a pressurised propellant to at least in part enable spray generation. A widely used option has been the use of VOCs, such as liquefied hydrocarbons or chlorofluorocarbons, to pressurise the liquid composition. However, it is increasingly recognised that the addition to the atmosphere of VOCs/greenhouse gases may have detrimental environmental consequences.
Other marketed domestic spray devices involve the use of hand-powered mechanical mechanisms, such as squeeze spray and trigger spray devices, to enable spray generation. Unfortunately, such mechanisms suffer the inherent problem of requiring physical effort on the part of the consumer. In addition, devices utilising this mechanism or simple variants thereof tend not to produce good quality sprays. Solutions to the problems encountered with the above spray devices have been suggested, certain of which involve the use of alternative atomisation techniques. Thus, numerous patents refer to the possible use of electrostatic atomisation, where spray generation is brought about by subjecting the liquid to be sprayed to a high electric potential. Certain other patents refer to the possibility of ultrasonic atomisation, which utilises high frequency vibrational energy to break up a liquid into discrete droplets.
A further ‘alternative’ atomisation technique is that of effervescent atomisation, where gas is bubbled into a film of liquid causing it to break up into discrete droplets. Most of the work in this area has related to fuel atomisation, particularly in the automobile industry [see, for example, U.S. Pat. No. 5,730,367 (Pace and Warner)]. However, U.S. Pat. No. 5,323,935 (Gosselin et al) appears to describe a domestic spray device that may operate by effervescent atomisation, at least in one of the embodiments of the invention. Use of this atomisation technique overcomes many of the problems of conventional domestic spray devices, as described above. The devices described by Gosselin et al create the required air flow by manually pressurising an air pressure chamber. In practice, this means that the air can only be used in discrete quantities before the air pressure has to be recharged. In addition, the air to liquid mass ratio that can achieved is limited by such discrete feed pumping means—U.S. Pat. No. 5,323,935 claims only between 0.01:1 and 0.06:1.
The present invention involves the use of a continuous feed gas pump, typically an electrically powered pump. The use of such pumps in spray devices is described in U.S. Pat. No. 5,192,009 (Hildebrandt et al) and U.S. Pat. No. 5,046,667 (Fuhrig); however, the spray devices described in these patents do not utilise effervescent atomisation. Hildebrandt discloses a known nozzle in which fluid (liquid) is introduced through tangential ducts and is broken up by air from an air inlet opening. Fuhrig discloses a nozzle in which air is supplied via a two component vortexing system and is fed orthogonally to the edge of a central liquid stream. Neither of these publications suggests the benefits attained by the use of a continuous feed gas pump with an effervescent atomisation spray device.